[email protected] (Dave Williams)
fords  24 Mar 1994

-> Not me; I don't have that data.

Whoops, it was Brian Kelley, replying to one of your messages.  Sorry
about that.


-> As Dan Malek's numbers demonstrated.  But isn't there a lot to be
-> gained from duration, even if the max lift is low?

Yes, but we were talking about lift specifically, not duration.  They
sort of go hand in hand, though.  For example, let's say you have a port
that flows great at .400 and lift starts falling off at .450 - it can
happen if you have a chamber shrouded just the right way.  Ideally you'd
have a square lobe that'd pop the valve to .400 and hold it there.
Practically you can't do that without launching the valve out of the
head, so you overshoot your .400 figure to whatever it takes to keep the
lifters, pushrods, rockers, and valves together.  (the knee-bone's
connected to the leg-bone, etc...)  The tremendous weight of the Ford
hydraulic rollers and the wimpy springs mean you're seeing higher "lift"
figures than the cam grinders would otherwise put in there.


-> Does going to roller rockers, specifically higher ratio rockers,
-> improve this situation at all?

The higher ratio will help by making the spring "look" stiffer to the
cam.  Valve velocity will be up, but lifter and pushrod velocity will be
down.  If you knew the cam was going to be used with 1.7 rockers you
could be a little more aggressive on the profile without causing valve
float problems.

Lift and duration are just guidelines.  What you're after is area under
the profile's curve.  Well, that's maybe a little simplistic, but it'll
do.